There are many forms of tablet digitizers, but these digitizers traditionally have a tether which couples the stylus to the system, are not cost effective or have other disadvantages.
There are pressure-sensitive input apparatus proposals, such as that disclosed by U.S. Pat. No. 4,929,934 issued May 29, 1990 to Ueda et al, where there are disposed a complex array of x and y coordinate resistive members connected to mutually parallel electrodes for detecting a point depressed by a stylus or finger
U.S. Pat. No. 4,934,470 disclosed a data input board for detecting of coordinates of a writing tip which included a rigid and an elastic plate with electrically conductive surfaces Another x-y coordinate system is illustrated by the electrographic touch sensor of U.S. Pat. No. 4,731,508 issued Mar. 15, 1988 to Gibson et al. Some have proposed a cordless pen which would emit a directional electric field from the tip of a pen stylus which is capacitively coupled to an embedded X and Y coordinate system in a digitizer tablet which is scanned by a microprocessor, such as that shown by U.S. Pat. No. 4,672,154 issued June 9, 1987 to Rodgers et al., a system similar to the coordinate coil stylus system of U.S. Pat. No. 3,904,822 of Sept. 9, 1975 to Kamm et al.
Also in the keyboard art, piezoelectric polymer keyboards have been formed which are non-contact. These include U.S. Pat. No. 4,633,123 issued Dec. 30, 1986 to Peter F. Radice, where a piezoelectric PVDF film is adhered to a pair of electrically insulating substrates having rows and columns to form a switch.
Position detectors in the form of infrared and ultrasound transducers have been used to detect position, such as those described in U.S. Pat. No. 4,758,691 issued July 19, 1988 to De Bruyne. De Bruyne suggests that the fixed electrode of the ultrasound transducer can be used as a digitizer. He claims a fixed electrode formed by PVDF plastic foil which is metallized on its inner surface.
In addition, representative of those systems with a wired stylus are U.S. Pat. Nos. 3,591,718 issued July 21 6, 1968 to Assano et al; 4,806,918 issued Feb. 21, 1989 to Berke et al; 4,818,826 issued Apr. 4, 1989 to Kimura et al; 4,752,655 issued June 21, 1988 to Tajiri et al; and 4,947,156 issued Aug. 7, 1990 to Sata et al.
Also illustrative of the state of the art are the following IBM Technical Disclosure Bulletins: Check Pad for Personal Computer, Vol 30, No. 3, Aug. 1987; Personal Identification Terminal, Vol 31, No. 7, Dec. 1988; Pressure Sensitive Cursor Control Keypads, Vol. 31, No. 12, May 1989; Cursor Controller/Graphics Pad, Vol 28, No. 9, February 1986; Manual Character Entry Devices, Vol. 19 No. 6, Nov. 1976 ; Three-axis Touch Sensitive Pad, Vol. 29, No. 8, Jan. 1987.